Retention Of Mercury Research Articles

Potential of Brass to Remove Inorganic Hg(II) from Aqueous Solution through Amalgamation.

Brass shavings (CuZn45) were tested for their efficiency to remove Hg(II) from contaminated groundwater through amalgamation. The study was focused on long-term retention efficiency, the understanding of the amalgamation process and kinetics, and influences of filter surface alteration. Column tests were performed with brass filters (thickness 3 to 9 cm) flushed with 1000 μg/L Hg solution for 8 hours under different flow rates (300 to 600 mL/h). Brass filters consistently removed >98% of Hg from solution independent of filter thickness and flow rate. In a long-term experiment (filter thickness 2 cm), Hg retention decreased from 96 to 92% within 2000 hours. Batch and column experiments for studying kinetics of Hg removal indicate ~100% Hg removal from solution within only 2 hours. Solid-phase mercury thermo-desorption analysis revealed that Hg(0) diffusion into the brass surface controls kinetics of mercury retention. Brass surface alteration could be observed, but did not influence Hg retention.

Nanostructured and Selective Filter To Improve Detection of Arsenic on Surface Plasmon Nanosensors

The development of a pretreatment system to assist surface plasmon sensor-based measurement of arsenic in water is described. The system proposed addresses important issues, regarding the reliable in situ detection of arsenic in water. This system uses a primary filter made of nonactivated cotton fibers for particulate matter and chemical retention agents without modifying the arsenic concentration in the water sample. A secondary filter was designed for retention of mercury, lead, and other heavy metals without alteration of the arsenic concentration in the collected water samples to be sensed. This filter was made with amino-functionalized carbon nanotubes. The results of the operational assessment of this filter show a retention efficiency of 98% for suspended solids, 96% for mercury ions, and 2% for arsenic, a remarkable improvement toward the accurate detection and quantification of arsenic in contaminated waters.

Batch process of polymer-enhanced ultrafiltration to recover mercury (II) from wastewater

The removal of mercury (II) from water by polymer-enhanced ultrafiltration (PEUF) was carried out using polyethylenimine (PEI), polyvinylamine (PVAm) and poly(acrylic acid) (PAA) as the metal-binding polymers. All three water-soluble polymers had strong interactions with mercury (II) in aqueous solutions, and a high mercury rejection was achieved with PEUF. At a given polymer dosage, the permeate flux followed the order of PVAm > PEI > PAA, presumably due to different physiochemical properties (e.g., viscosity and interfacial property) of the solution systems. Membrane fouling by PVAm and PEI in cross-flow mode was insignificant, but the flux decline due to fouling by PAA was not negligible. The batch operation of PEUF was modeled based on mass balance, and the applicability of the model equations was validated with experimental data. For a given system, the mercury content in the concentrated retentate, the mercury retention rate, the batch time and membrane area needed to achieve a desired separation task could be predicted if prior knowledge of concentration dependences of permeate flux and solute rejection were known. The effects of the amount of feed solution to be treated per unit membrane area on the separation performance of batch PEUF was analyzed.

Effect of fly ash composition on the retention of mercury in coal-combustion flue gas

Fly ash from coal-fired power plant has been reported to be a promising sorbent for mercury capture. However, the nature of the Hg–fly ash interaction is still unknown. In this work, the thermal decomposition method is used to evaluate the effect of the fly ash composition on the retention of mercury in coal-combustion flue gas. Eight fly ash samples were collected from the electrostatic precipitators of eight full-scale pulverized coal-fired power plants. The high-temperature treatment is performed to gradually decompose the carbon and mercury species in the fly ashes, and each fly ash are divided into four groups. The content of the carbon and mercury present in all the examined samples was measured. The results show that the most mercury species are decomposed from the fly ash at 300°C. The quantity of carbon in the fly ash alone does not determine the amount of mercury retained at any temperature. The decomposed mercury content is related to the mercury content of the fly ash. The carbon particle with ultra-strong mercury capture capacity cannot be found in the fly ash. Furthermore, X-ray fluorescence spectrometry (XRF) is used to identify the elemental composition of inorganic components of all the native fly ashes. Multivariate linear regression method is used to assess the dominated components that determine the mercury retention capacity of these fly ashes. The results indicate that the carbon, silicon, iron, sulfur, and magnesium in fly ash all play a major role in mercury retention. Hence, both carbon and inorganic components influence the retention of mercury in the fly ash.

Chemical forms of the fluorine, chlorine, oxygen and carbon in coal fly ash and their correlations with mercury retention

Fly ashes recovered from the particulate control devices at six pulverized coal boiler unites of China, are studied using an X-ray photoelectron spectroscopy (XPS) with a particular focus on the functionalities of fluorine (F), chlorine (Cl), carbon and oxygen on fly ash. It is found that the inorganic forms of F and Cl are predominant on the ash surface in comparison with their organics, and the proportion of organic Cl is relatively higher than that of organic F. Similar results are also obtained in the bulk by correlating the F and Cl contents with those of the unburnt carbon and other compositions in ash. Strong correlations of mercury retention with surface carbon–oxygen functional groups indicate that the CO, OH/CO and (OCO)O on surface are of significant importance for mercury retention in fly ash. Their surface concentrations are related to coal type. The presence of Cl in fly ash helps with mercury retention. No obvious effect of F is observed.

Influence of Flue-Gas Components on Mercury Removal and Retention in Dual-Loop Flue-Gas Desulfurization

Due to the system, the dual-loop wet limestone flue-gas desulfurization process is assumed to be well-suited for mercury retention. As the behavior of mercury in the dual-loop process has been insufficiently dealt with in literature so far, the influence of sulfur dioxide and halides on mercury removal and retention was investigated. The process conditions in the loops are highly relevant for the removal and retention of mercury. The circulating slurries there differ in pH-value and oxidation–reduction conditions as well as in halides and sulfite concentrations and solid compositions. This work presents investigations that were conducted at a laboratory-scale test rig treating the flue gas of a pulverized coal combustion facility. The share of the removal of mercury in both loops was investigated as well as the removal of oxidized mercury compounds, the mercury re-emission, and the total mercury removal efficiency. Both loops showed comparable removal rates of oxidized mercury compounds. In the quencher, the removal and retention of mercury is assumed to be improved by the formation of stable mercury complexes with chloride. The decomposition of mercury complexes formed with sulfite and redox reactions are supposed to decrease mercury retention in the absorber. A higher sulfite concentration in the quencher induced by higher SO2 concentration in the flue gas can increase mercury removal by the enhanced formation of mercury complexes with sulfite. At the same time it can promote re-emissions due to a higher share of sulfite on total S(IV) at the resulting higher pH-value of the quencher. Furthermore, high S(IV) concentrations might result in an increased mercury adsorption on particles. Increased chloride concentrations in the absorber can lead to higher removal rates of sulfur dioxide and improved mercury retention as well as to relatively high shares of mercury in wastewater, whereas the latter constitutes the desired mercury pathway.

Accumulation and oxidation of elemental mercury in tropical soils

The role of chemical and mineralogical soil properties in the retention and oxidation of atmospheric mercury in tropical soils is discussed based on thermal desorption analysis. The retention of gaseous mercury by tropical soils varied greatly both quantitatively and qualitatively with soil type. The average natural mercury content of soils was 0.08±0.06μgg−1 with a maximum of 0.215±0.009μgg−1. After gaseous Hg0 incubation experiments, mercury content of investigated soils ranged from 0.6±0.2 to 735±23μgg−1, with a mean value of 44±146μgg−1. Comparatively, A horizon of almost all soil types adsorbed more mercury than B horizon from the same soil, which demonstrates the key role of organic matter in mercury adsorption. In addition to organic matter, pH and CEC also appear to be important soil characteristics for the adsorption of mercury. All thermograms showed Hg2+ peaks, which were predominant in most of them, indicating that elemental mercury oxidized in tropical soils. After four months of incubation, the thermograms showed oxidation levels from 70% to 100%. As none of the samples presented only the Hg0 peak, and the soils retained varying amounts of mercury despite exposure under the same incubation conditions, it became clear that oxidation occurred on soil surface. Organic matter seemed to play a key role in mercury oxidation through complexation/stabilization of the oxidized forms. The lower percentages of available mercury (extracted with KNO3) in A horizons when compared to B horizons support this idea.

Mercury Retention by Fly Ashes from Oxy-fuel Processes

The objective of this study is to determine the mechanism of mercury retention in fly ashes, the main solid waste from coal combustion power plants, and to evaluate the interactions between the type of mercury and fly ashes. The work was based on the results of mercury speciation in the gas and the solid fly ash before and after mercury retention. The identification of the mercury species in the gas was performed using previously validated methods, but the speciation of the mercury retained in the fly ashes was carried out using a mercury temperature-programmed desorption technique (HgTPD) still under development. The fly ashes were sampled from conventional coal combustion in air and oxy-combustion power plants. The main mercury species identified in the raw fly ashes and after they were subjected to an oxy-combustion atmosphere were mercury bound to organic matter and HgS, the ratio of these species depending on the characteristics of the ashes. The results obtained indicate that fly ashes are the route of mercury oxidation in an oxy-combustion atmosphere, although they hardly retain any mercury unless the unburned carbon content is high. HgTPD analysis shows that the main mechanism for mercury retention in the fly ashes is via the carbon matter.

CHARACTERIZATION OF FLY ASH FROM COAL-FIRED POWER PLANT AND THEIR PROPERTIES OF MERCURY RETENTION

Recent research has shown that fly ash may catalyze the oxidation of elemental mercury and facilitate its removal. However, the nature of mercury-fly ash interaction is still unknown, and the mechanism of mercury retention in fly ash needs to be investigated more thoroughly. In this work, a fly ash from a coal-fired power plant is used to characterize the inorganic and organic constituents and then evaluate its mercury retention capacities. The as-received fly ash sample is mechanically sieved to obtain five size fractions. Their characteristics are examined by loss on ignition (LOI), scanning electron microscope (SEM), energy dispersive X-ray detector (EDX), X-ray diffraction (XRD), and Raman spectra. The results show that the unburned carbon (UBC) content and UBC structural ordering decrease with a decreasing particle size for the five ashes. The morphologies of different size fractions of as-received fly ash change from the glass microspheres to irregular shapes as the particle size increases, but there is no correlation between particle size and mineralogical compositions in each size fraction. The adsorption experimental studies show that the mercury-retention capacity of fly ash depends on the particle size, UBC, and the type of inorganic constituents. Mercury retention of the types of sp2 carbon is similar to that of sp3 carbon.

Temperature programmed desorption as a tool for the identification of mercury fate in wet-desulphurization systems

In this study a thermal desorption procedure (HgTPD) was used to identify mercury species in samples of gypsum obtained from wet flue gas desulphurization plants (WFGD). Gypsum from industrial coal combustion power plants and gypsum from a laboratory device that simulates mercury retention in the WFGD process were studied. It was concluded that mercury sulphide (HgS) is the mercury species present in WFGD gypsums unless an additive is used. Mercury speciation in this kind of residue can contribute to a better understanding of the reaction and adsorption behaviour of mercury species in the WFGD process and provide a deeper knowledge of the environmental impact caused by the disposal or reuse of these Hg-containing residues.

Impact of oxy-fuel combustion gases on mercury retention in activated carbons from a macroalgae waste: Effect of water

The aim of this study is to understand the different sorption behaviors of mercury species on activated carbons in the oxy-fuel combustion of coal and the effect of high quantities of water vapor on the retention process. The work evaluates the interactions between the mercury species and a series of activated carbons prepared from a macroalgae waste (algae meal) from the agar–agar industry in oxy-combustion atmospheres, focussing on the role that the high concentration of water in the flue gases plays in mercury retention. Two novel aspects are considered in this work (i) the impact of oxy-combustion gases on the retention of mercury by activated carbons and (ii) the performance of activated carbons prepared from biomass algae wastes for this application. The results obtained at laboratory scale indicate that the effect of the chemical and textural characteristics of the activated carbons on mercury capture is not as important as that of reactive gases, such as the SOx and water vapor present in the flue gas. Mercury retention was found to be much lower in the oxy-combustion atmosphere than in the O2+N2 (12.6% O2) atmosphere. However, the oxidation of elemental mercury (Hg0) to form oxidized mercury (Hg2+) amounted to 60%, resulting in an enhancement of mercury retention in the flue gas desulfurization units and a reduction in the amalgamation of Hg0 in the CO2 compression unit. This result is of considerable importance for the development of technologies based on activated carbon sorbents for mercury control in oxy-combustion processes.

Application of mercury temperature programmed desorption (HgTPD) to ascertain mercury/char interactions

This work investigates the scope of a mercury temperature programmed desorption (HgTPD) technique for identifying mercury species in solids. The specific objective of this study was to clarify the mechanism of mercury retention by chars used as sorbents in coal combustion in air and oxy-combustion atmospheres based on the identification of the mercury species retained. Different mercury species were identified by HgTPD depending on the flue gas composition and the type of char. The results led to the conclusion that depending on these conditions the main mechanism of mercury retention will be the interaction of mercury with organic matter, or the interaction of mercury with sulfur to form HgS. In a few particular cases Hg2(NO3)22H2O was produced on the char surface. It was found that HgTPD is a highly useful technique for investigating the different mechanisms of mercury/char/gas interactions.

Mercury photochemistry in snow and implications for Arctic ecosystems

Mercury is a toxic and bioaccumulative environmental contaminant, which may be transported to remote regions around the world, such as the Arctic. Snowmelt is a major source of mercury to many surface water environments, but the amount of mercury in snow varies considerably. This variation is due to the balance of mercury retention and losses from snow, which is largely controlled by photochemical mechanisms controlling speciation. As such, quantifying these photochemical reaction rates and the factors affecting them will allow for the prediction of mercury speciation and movement into receiving water bodies. This will consequently improve our ability to predict exposure of aquatic organisms to mercury. This review highlights knowledge gaps in the quantification of mercury photochemical kinetics and the specific research required to advance the science of mercury photochemistry in snow, while examining the physical and chemical snowpack variables that influence snowpack mercury reactions. At present, our lack of mechanistic and kinetic knowledge of mercury reactions in snow is one of the greatest gaps preventing accurate predictions of mercury fate in regions containing seasonal snowpacks.

Activated carbons from biocollagenic wastes of the leather industry for mercury capture in oxy-combustion

This study evaluates the capacity of a series of activated carbons obtained from leather industry waste to retain mercury. The behavior of these materials was compared in two simulated flue gas compositions at laboratory scale. The atmospheres were (i) a typical coal oxy-fuel combustion atmosphere and (ii) an O2+N2 atmosphere. The activated carbons displayed different behaviors depending on their characteristics and the gas composition. The best results were obtained for the activated carbon with the highest surface area and greatest amount of micropores, sulfur and acidity character, these results being comparable to those of an activated carbon impregnated with sulfur specifically designed for capturing elemental mercury. The highest level of mercury retention was achieved in a O2+N2 atmosphere. However, independently of the ability of these materials to capture mercury, their most interesting characteristic was their ability to oxidize mercury in an oxy-combustion atmosphere, since this would facilitate the retention of mercury in flue gas desulfurization units with the consequence that the risk of damage to the CO2 compression and purification units would be reduced or even removed.

Influence of a CO2-enriched flue gas on mercury capture by activated carbons

The main environmental problem caused by the production of energy from coal combustion is the emission of CO2. One emerging technology designed for CO2 capture is oxy-combustion. Among other issues to be solved in oxy-combustion power plants is the presence of mercury as this may damage the CO2 compression unit. Hence the study of the behavior of mercury in oxy-combustion is of great interest both from an environmental and a technological point of view. The present study performed at laboratory scale evaluates the retention of mercury in a CO2-enriched flue gas using the same activated carbon before and after it has been impregnated with sulfur and proposes a mechanism to explain the interactions between mercury and activated carbons. The results show that carbonyl and quinone groups are responsible for mercury oxidation and retention in the carbons. Although the contact time between mercury and the activated carbon surface limits the amount of mercury that can be captured, high retention capacities can be achieved in an oxy-combustion atmosphere. The presence of water, in high concentrations in oxy-combustion, may compete for the same active sites (carbonyl groups) as mercury, thereby inhibiting mercury adsorption on the surface of the activated carbons. Moreover, the presence of sulfur in the impregnated material, which is the key to mercury capture in other atmospheres, does not modify mercury capture in oxy-combustion.

Gaseous mercury behaviour in the presence of functionalized styrene–divinylbenzene copolymers

Abstract Two styrene-6.7 % divinylbenzene copolymers functionalized with aminophosphonate groups and phosphonic acid groups by means of “one-pot” reactions were evaluated for gaseous mercury removal. The results were compared with those obtained using a commercial activated carbon. These materials exhibit a significant capacity for mercury oxidation (13–25 %) with low mercury capture (9–30 μg g–1). The mercury retention capacity was observed to decrease when acid gases are present in the gas atmosphere. The highest retention capacity corresponded to the highest oxidation ratio and was obtained using the AMINOPHOS sample. These results suggest a mercury oxidation and a subsequent chemical adsorption mechanism in which the amino groups play a role in mercury capture.

Mercury capture by a regenerable sorbent under oxycoal combustion conditions: Effect of SO2 and O2 on capture efficiency

The present study evaluates an Au/C sorbent based on the direct reduction of a gold salt on a carbon coated structured cordierite monolith for mercury capture under oxyfiring conditions. Both mercury retention efficiency and mercury retention capacity were tested in a bench scale plant under different conditions. The influence of gas temperature (50–150°C) and gas composition (CO2, N2, SO2, and O2) on sorbent performance for mercury capture is evaluated and discussed. The amount of mercury captured did not vary significantly with temperature under a CO2 atmosphere. These results were compared with those obtained under N2 atmosphere with no remarkable differences found between them. High retention efficiencies were obtained despite the small amount of gold used. The presence of SO2 and O2 in the flue gas led to mercury oxidation that seemed to be mainly promoted by SO2 under the presence of the Au-sorbent.

Speciation of Hg retained in gasification biomass chars by temperature-programmed decomposition

The development of elemental mercury (Hg0) capture technology for coal-fired power plants is essential for achieving the goal of zero emissions from coal derived flue gas. Sorbents such as biomass gasification chars have proved to be effective for mercury capture and offer the added advantage of their low cost since they are sub-products of the thermal conversion process. However, the mercury species captured on the sorbents have not yet been characterized. In this study, a temperature programmed decomposition technique was used to identify the mercury species captured on the sorbents and to clarify the mechanisms responsible for mercury retention. The mercury species formed were observed to be dependent on char characteristics and flue gas composition. The results showed that mercury chloride was the most likely mercury species in a simulated coal combustion atmosphere from the chars obtained from poultry litter, sunflower husks and paper and plastic waste, the last two containing small amounts of mercury sulphate. The mercury compounds identified in the char from the gasification of wood waste were mainly sulphide and sulphate species.

Mixtures including wastes from the mussel shell processing industry: retention of arsenic, chromium and mercury

Abstract Three mixtures containing ashes from the mussel shell calcination industry, sewage sludge, wood ash and/or mussel shell were studied. Such wastes are difficult to recycle individually, but performing adequate mixtures could aid to solve this problem. Two mixtures included different percentages of mussel shell calcination ashes, sewage sludge and mussel shell, while the third was composed by mussel shell calcination ashes, sewage sludge and wood ash. Adsorption was very high for some pollutants: 98–99% for Hg, and 90–96% for As, while it was not higher than 32% for Cr. The pH values in the mixtures showed a clear diminution in the alkalinity of the shell ashes. Further, a drastic reduction of the extreme electric conductivity of these ashes occurred. The carbon/nitrogen ratio in the mixtures clearly improved when compared with the individual wastes. The nutrient content was similar in the three mixtures. The heavy metals concentrations were low in all three mixtures. Calcite was the most prevalent crystalline compound (≥83%) and aragonite was greater than 3.7%. In view of these results, using such mixtures would facilitate the treatment and recycling of shell calcination ashes, as well as other wastes. The mixtures could be useful in degraded environments, such as mine dumps, due to their nutrient content and the adsorption potential for Hg and As.

Investigation on mercury reemission from limestone-gypsum wet flue gas desulfurization slurry.

Secondary atmospheric pollutions may result from wet flue gas desulfurization (WFGD) systems caused by the reduction of Hg2+ to Hg0 and lead to a damping of the cobenefit mercury removal efficiency by WFGD systems. The experiment on Hg0 reemission from limestone-gypsum WFGD slurry was carried out by changing the operating conditions such as the pH, temperature, Cl− concentrations, and oxygen concentrations. The partitioning behavior of mercury in the solid and liquid byproducts was also discussed. The experimental results indicated that the Hg0 reemission rate from WFGD slurry increased as the operational temperatures and pH values increased. The Hg0 reemission rates decreased as the O2 concentration of flue gas and Cl− concentration of WFGD slurry increased. The concentrations of O2 in flue gas have an evident effect on the mercury retention in the solid byproducts. The temperature and Cl− concentration have a slight effect on the mercury partitioning in the byproducts. No evident relation was found between mercury retention in the solid byproducts and the pH. The present findings could be valuable for industrial application of characterizing and optimizing mercury control in wet FGD systems.